1. Field
This application relates to fiber optic cable testers in general, and more particularly visual continuity, attenuation and optical loss testers that are used to troubleshoot and inspect fiber optic cable installations.
2. Prior Art
Previously, there have been many solutions and techniques introduced to test optical fiber cables. Commonly used methods can be categorized as follows:
(a) OTDR (Optical Time Domain Reflectometer)
An OTDR is used to characterize optical power reflected along optical fibers with a graphical signature on a display screen. The OTDR has the capability to measure the length of the optical fiber and characterize the optical power loss between any two points along the optical fiber. This equipment is built with highly sophisticated and sensitive electronic components. The OTDR, which only requires access to one end of the optical fiber, sends pulses of light into an optical fiber and measures the strength of the power reflected to the instrument. The OTDR takes thousands of measurements and displays the average of the returned power levels on the screen as a characteristic trace. The trace forms a line with a negative slope from left to right.
OTDR is the most expensive field testing equipment for optical fiber cables. Furthermore, the equipment requires periodic factory calibration to keep up with industrial test standards. The persons who use the equipment also require a high level of technical training which is usually provided by the same manufacturer of this equipment. Another disadvantage is that OTDR only tests one strand at a time, which is very time consuming in high volume applications.
(b) Power Meter (Cable Analyzer, Certifying Tester)
This category offers optimum cost for field testing of optical fiber cables compared to the OTDR. The principle technique is using an optical transmitter (light source) at one end of the cable, and optical receiver (power meter) at the other end of the cable. This technique is also known as end-to-end attenuation testing. An attenuation tester measures the optical power loss between cable termination points. Acceptable loss values are established according to the link loss budget for the cable under test. A specific type of optical jumper patch cord is required between the permanent link (the optical cable under test) and the testers (transmitter and/or receiver). A reference value (field calibration) is required prior to testing. If the jumper cables are dirty, the reference value will be higher and the attenuation measurement will not be accurate. Furthermore, jumper cables must have the same core size as the optical fiber cable (permanent link) being tested. If the jumpers are disconnected or the equipment is turned off after the field calibration process, the reference value is no longer valid and the testers should be recalibrated. Before calibrating, the testers should be left on for 10 to 15 minutes to let the drivers stabilize. The testers should come to the temperature at which they will be used before calibrating, since driver output can change with temperature. If the testers have been sitting in a hot van in the summer, or overnight in the winter, this may take an hour or more. The testers should be recalibrated after any event that can affect the amount of light being injected into the optical fiber, including disconnecting, reconnecting, changing the jumper cables, or replacing the batteries, etc. Good batteries can also be important for accurate test results. As batteries get weaker, the voltage may drop, and some testers will begin to give erratic results before the testers stop operating completely. If the testers use disposable batteries, it is unlikely anyone will keep the track of when the batteries were replaced. To achieve the most accurate loss measurements during calibration and testing, a multimode launch cord is required and should be wrapped five times (non-overlapping) around the mandrel before calibration. The diameter of the mandrel is also an important factor. If a mandrel does not exist during the time of testing, the consistency of the test results will be suspicious.
Another disadvantage is that end-to-end loss measurement requires testing one or two strands at a time, which is very time consuming in high volume applications. Moreover, two trained technicians are required at each end of the cable being tested. The technicians often use wireless devices (e.g. mobile phones, radios) to communicate during a troubleshooting operation which can cause interference with the field test instruments during testing and report inaccurate test results.
(c) Visual Light Source
A visual light source is also called an optical fiber light emitting diode (LED) or optical flash light. It also is in the category of continuity testers which test and troubleshoot the linkage of optical fiber strands. By connecting an optical fiber flashlight to one end of an optical fiber strand and then looking at the other end, a technician can determine if there is a breakage in the strand when the light is not visible.
However, cleanliness is the biggest concern and mostly overlooked factor during troubleshooting. Every optical fiber testing practice dwells on cleanliness for good reason—poor cleanliness practices are the single greatest cause of problems in optical fiber testing and operation. Cleaning optical fiber connectors requires lint-free paper or 99% reagent grade isopropyl. Alcohol from a drugstore may look and smell the same and show isopropyl on the label, but it is often only 70% pure—plenty of room for impurities. The wipes must be lint-free and made for this type of work. If using canned air to blow adapters clean, it should be made specifically for this purpose—keyboard cleaners from an office supply store can have many impurities. To clean an optical fiber connector, the test technician should wipe the connector ferrule with an alcohol dampened wipe—the alcohol helps dissolve dirt that may be on the ferrule. After cleaning with the moist wipe, the ferrule must be polished with a clean dry wipe to remove the alcohol and dissolved dirt. If the ferrule is allowed to air dry without polishing, the dirt in the alcohol is redeposited on the ferrule. After cleaning, the technician should put a dust cap on the connector immediately. This prevents damage to the ferrule and helps reduce contamination.
There is dust in the air all the time, and the cleaning process itself may create a slight electrostatic charge on the connector that can attract dust out of the air. A capped connector should also be cleaned before plugging it in—the plastic in same caps can deposit contamination on a ferrule. The end face of a ferrule should never be touched during testing—even “clean” fingers will leave an oily coating on a ferrule. Dust covers should be kept on all adapters until immediately before a connector is to be inserted. If a technician receives a failing test result for one link, the fiber optic connector should not be plugged into another adapter for comparison without cleaning it first—contamination can easily be spread from one adapter port to another. It is especially important to keep the port in pre-terminated cassettes clean. Unlike traditional optical fiber cabinets that allow a technician to unplug a connector on the inside for cleaning, pre-terminated cassettes are generally factory sealed, making ports difficult to clean if contaminated. This is also true of the MPO ribbon connectors on the back of the cassettes—they are difficult to clean once they are contaminated. Some suppliers now offer an advancing-tape cleaner that can be inserted into an adapter or female connector, but they are not always completely successful.
Because of the above concerns, it is more affective and more economical to keep the fiber adapters and ports clean from the very beginning.
Issued U.S. Pat. No. 5,196,899—Serwatka, is a good example for the above concerns. Serwatka described an embodiment in his patent application that consists of multiple connector adapters or adaptive interfaces for a polarity of connector types to match or connect various fiber optic connectorized endings, and also a bare fiber to a light source. The adaptive interface comprises a wheel having a variety of fiber optic connectorized end fittings.
From the perspective of cleanliness and a micro sensitive nature of optical fiber testing standards, dust is easily carried each time a fiber optic connector is plugged and unplugged from an optical adapter (or connectorized end fitting). The dust can easily cause attenuation (optical loss) during operation. Since Serwatka's apparatus contains a mechanical wheel to match different connector endings (fiber optic adapters), the dust can be accumulated inside the apparatus and carried easily from one connector to another during the continuity test.
The other disadvantage with Serwatka's apparatus is that when the mechanical wheel is aligned with the light source, only two connector endings can be tested at a time. Therefore, having multiple connector adapters does not speed up the test if the cables being tested have the same type all over. In today's fiber optic installation best practices, only one type of connector and adapter is used for an entire site to provide user flexibility and ease of operation. Therefore, Serwatka's approach is not an ideal solution for rapid field testing in high volume of test conditions. Thus, because of the fragile nature of fiber optic strands, someone with no technical experience can easily break the fiber optic strand while using Serwatka's apparatus by exceeding the maximum allowed bend radius. The optimum solution should be not touching the permanent link (fiber optic linkage being tested) in the field.
Similarly, issued U.S. Pat. No. 7,373,069—Lazo claims at least two fixed adapters as a part of his tester. Therefore, his invention is also affected by the cleanliness concerns described above and potential fiber damage while plugging and unplugging the fiber optic connectors during the test.
Present application and described embodiment resolves all the problems associated with the above concerns.
(d) VFL (Visual Fault Locator), VFF (Visual Fault Finder)
A visual fault locator or finder operates in the visible laser light range. It's used to identify individual optical fibers within a cable by sending a red laser light down the optical fiber. When used as a troubleshooting tool, the optical fiber strand will glow red at the point of a break or separation of optical fibers. Units that pulse on/off are easier to use when looking for a break. These tools can also be used to detect a damaged optical fiber ferrule. If the ferrule is cracked or damaged, the entire ferrule will glow red during this test.
However, laser light sources can cause eye damage. A person should never look at optical fiber strands with a visible or invisible laser light source on.
The other problem with the VFL and VFF that they offer only testing on one connector or port at a time, which is time consuming. If the fiber optic strand is broken inside a thick fiber optic cable jacket, innerduct or conduit, the laser light will not be noticeable. These testers offer either a fixed adapter tip or interchangeable port for different types of fiber optic connectors. Therefore, dust is carried easily from one connector to another during field testing of optical fiber connectors.
(e) Strand Identifier
A clamp-on unit inserts a macrobend into the optical fiber cable and thereby is able to detect the light escaping from the optical fiber. This device is used to detect the presence of light, as well as transmit and receive direction on singlemode and multimode optical fiber cable.
However, because of creating a macrobend into the optical fiber strand being tested, this device can break the fiber easily if accidentally used on fragile hot spots. The test technician could never know which sections of the fiber cable might have fragile spots. Moreover, this tester is considerably costly to buy and operate.
(f) Fiber Optic Microscope
A hand-held or desktop microscope with different magnifying rates, such as 250×, 300×, 400× is a well known optical instrument to visually check the surface of a fiber optic core and cladding on terminated and polished fiber optic ferrules. The fiber optic microscope also comes with a fixed or interchangeable adapter interface where the fiber connector plugs in. Therefore, dust is easily carried from one connector to another during inspection. Furthermore, labor cost becomes high since only one strand or port can be inspected at a time.
As it can be clearly seen from all the disadvantages of the prior arts, presently there has been no solution offered to provide the following advantages of the present application:                (a) Rapid field testing,        (b) Dust free application,        (c) Visual light source for eye protection,        (d) No field or factory calibration is necessary,        (e) No certified or trained technicians are required,        (f) No patch cords or jumpers are needed,        (g) No receiving device at the opposite end of the cable is required,        (h) Multiple fiber connectors can be tested all at once,        (i) No contact with fiber optic cable strands; therefore no potential risk for fiber breakages,        (j) Low cost of manufacturing and ownership,        (k) Ease of use,        (l) Labor saving is maximized,        (m) Compatible with all existing fiber optic adapters and panels.        
These and other advantages of one or more aspects will become apparent from a consideration of the ensuing description and accompanying drawings of the present application.